The present invention relates to solid phase microextraction fiber structure, e.g., for preconcentrating trace organic materials from various matrices, and to a method of making such a solid phase microextraction fiber.
With ever increasing environmental and health concerns, the analytical capability for extraction and preconcentration of trace organic contaminants from aqueous, gaseous, and solid samples have become extremely important. Various forms of Soxhlet extraction,1 liquid-liquid extraction,2 accelerated solvent extraction,3 microwave-assisted solvent extraction,4 solid-phase extraction,5 supercritical fluid extraction,6,7 purge and trap,8 and other methods9-11 are traditionally used for this purpose. Some of these methods often employ large volumes of hazardous organic solvents, others are time-consuming, and/or expensive. Most of these methods require collection of the samples and their transportation to the laboratory for further processing. Incorrect sample handling during collection, transportation, and preservation may result in significant variability in analysis results. Solid-phase microextraction (SPME) technique, developed in 1989,12 effectively overcomes these difficulties by eliminating the use of organic solvent and by allowing sample extraction and preconcentration to be done in a single step. The technology is more rapid and simple than the conventional methods. It is also inexpensive, portable, and sensitive.
In SPME, the outer surface of a solid fused silica fiber (approximately 1 cm at one end) is coated with a selective stationary phase. Thermally stable polymeric materials that allow fast solute diffusion, are commonly used as stationary phases. The extraction operation is carried out by dipping the coated fiber end into the sample matrix, and allowing time for the partition equilibrium to be established. The amount of an analyte extracted by the coating is described by Nernst""s partition law.13 The sensitivity of the method, is mostly governed by the partition coefficient of an analyte between the coating and the matrix.14 Extraction selectivity can be achieved by using appropriate types of stationary phases that exhibit high affinity toward the target analytes. For liquid samples, stirring and salting out procedures are commonly used to aid the extraction process.15,16 
SPME is normally followed by gas chromatography (GC) analysis, in which the extracted analytes are thermally desorbed in the GC injection port for introduction into a GC column. Currently SPME has also been interfaced with other separation techniques, including high performance liquid chromatography (HPLC),17 and supercritical fluid chromatography (SFC).18 A specially designed syringe is commonly used to facilitate safe fiber handling during sample extraction and subsequent thermal desorption of the extracted sample in the injection port of a gas chromatograph.
Solid-phase microextraction is predominantly performed on SPME fibers coated with nonpolar poly(dimethylsiloxane) (PDMS) stationary phases.19-21 A significant drawback of such fibers is that their recommended operating temperatures are relatively low, and generally remain within the range of 200-270xc2x0 C.22 This is about 80-150xc2x0 C. lower than the upper temperature limit for the same stationary phases when used in a GC column. Two factors are believed to be responsible for this. First, the stationary phase coating thickness on an SPME fiber is a few orders of magnitude higher than the stationary phase film thickness in a GC column. Stabilization of such a thick film is much more difficult than that of submicrometer thick films used in GC columns. Second, the lack of proper chemical bonding of the stationary phase coating with the fiber surface may also be responsible for the lower thermal stability of conventionally coated PDMS fibers.
The problem should be more difficult for SPME fibers with conventionally coated polar stationary phases, since immobilization of physically coated polar films (even of submicrometer thickness) is much more difficult than that for nonpolar films.23,24 Achieving immobilization of thick polar coatings, as used in SPME, should be even more difficult. It is evident that future advancements in SPME technology should greatly depend on new scientific breakthroughs leading to the development of more efficient technologies for creating selective stationary phase coatings, and their chemical immobilization as thick films of enhanced operational stabilities (temperature, solvent, etc.).
The present invention provides a new and useful solid phase microextraction fiber structure and a new and useful method of making such a fiber structure. The present invention uses sol-gel chemistry to provide a simple and convenient pathway for the synthesis of advanced material systems and applying them as surface coatings.25,26 The sol-gel chemistry provides efficient incorporation of organic components into the inorganic polymeric structures in solution under extraordinarily mild thermal conditions.27 
Among the advantages of the use of sol-gel technology in connection with the present invention are: (a) low costs, (b) unique ability to achieve molecular level uniformity in the synthesis of organic-inorganic composites, and (c) strong adhesion of the coating to the substrate due to chemical bonding.28 The last of the above advantages is especially important for SPME.
A solid phase microextration fiber according to the present invention basically comprises a fiber, and a deactivated surface-bonded sol-gel coating on a portion of the fiber to form a solid phase microextraction coating on that portion of the fiber. The solid phase microextraction coating is capable of preconcentrating trace organic compounds in various matrices. The solid phase microextraction coating has the formula: 
wherein,
X=Residual of a deactivation reagent;
Y=Sol-gel reaction residual of a sol-gel active organic molecules;
Z Sol-gel precursor-forming element
l=an integer xe2x89xa70;
m=an integer xe2x89xa70;
n=an integer xe2x89xa70;
p=on integer xe2x89xa70;
q=an integer xe2x89xa70; and
(l, m, n, p and q are not simultaneously zero).
Dotted lines indicate the continuation of the chemical structure with X, Y, Z, or Hydrogen (H) in space.
The preparation of the solid phase microextraction fiber includes the steps of providing the fiber structure, providing a sol-gel solution comprising a sol-gel precursor, an organic material with at least one sol-gel active functional group, a sol-gel catalyst, a deactivation reagent, and a solvent system. The sol-gel solution is then reacted with a portion of the fiber (eg the tip of the fiber) under controlled conditions to produce a surface bonded sol-gel coating on the portion of the fiber. The fiber is then removed from the sol gel solution and is heated under controlled conditions to cause the deactivation reagent to react with the surface bonded sol-gel coating to deactivate and to condition the sol-gel coated portion of the fiber structure. Preferably, the sol-gel precursor includes an alkoxy compound. The organic material includes a monomeric or polymeric material with at least one sol-gel active functional group. The sol-gel catalyst is taken from the group consisting of an acid, a base and a fluoride compound, and the deactivation reagent includes a material reactive to polar functional groups (e.g., hydroxyl groups) bonded to the sol-gel precursor-forming element in the coating or to the fiber structure.
Additionally, the solid phase microextraction fibers made according to the present invention can be effectively used in combination with gas chromatography capillary columns and capillary electrochromatography columns described in concurrently filed U.S. Application Serial No. 60/102,483 entitled Capillary Column and Method of Making, incorporated herein by reference.